I just changed the oil pressure switch. Now I am getting around 30 psi on the gauge with the engine cold. What should the oil pressure be? If this is too low, is my next move to replace the oil pump?

Now we are getting somewhere. Pressure is a low when cold. I like to see psi over 40 when its cold. Most important, what'* your readings when engine is hot.

Oil pressure specs when engine is hot.

6 psig at 1,000 engine RPM

18 psig at 2,000 engine RPM

24 psig at 4,000 engine RPM

If your readings are lower, I am suspecting your oil pump is getting weak or you have a lot of sludge in the oil pan causing low pressure. More than likely a bad pump.

Oil pressure readings engine hot.
1,000 rpm -- 23 psi
2,000 rpm -- 25 psi
4,000 rpm -- 40 psi

I let it idle to get it to start ticking. There was no loss of pressure when the ticking started. Another thing that happened is that I shut it off for 10 seconds and then started it again and the ticking was gone. I didn't let it idle until it started ticking again. Is there a possibility that this sound is a fuel injecter?

I was wrong on the psi readings. They were actually.
1000 rpm -- 30 psi
2000 rpm -- 35 psi
4000 rpm -- 40 psi

Id say your ok on pressure. How long have you owned the vehicle? Oil changes done when needed? The reason I ask is these engine very rarely have lifter problems alone. I did have one avalanche with the 5.3 engine had bad lifter noise. The engine itself wasn't taken care of and was really nasty on the inside. I replaced all the lifters and added Riselone to the engine oil to help with the lifter noise. It took care of the noise after about 500 miles. You also need to remember the pistons in theses engine don't have very large piston skirts compared to the 5.7 liter. Some piston knock will be heard especially when cold.

I've had this yukon since 45,000 miles. It'* now at 145,000 miles. Serviced by the dealer every 5,000 miles.
Just sat in the drive thru for ten minutes idling then the ticking started. I shut off the car for a minute or so. Started it up and it ticked for a couple seconds and stopped even with idling for another few minutes.
Do you think it could be a fuel injector?

Unless it'* missfiring, but it'* not. At this point I would try adding some additive to the oil and see if that helps. This is goin off the notion all the internal engine components are ok. Riselone is a good product, available from any parts store. I don't like Lucas, it'* too thick.

do u have any lights on on the dash?

As far as I can tell all of the dash lights work. What are you getting at?
No check engine light comes on when the ticking starts, if that'* what you mean.

UPDATE--- I idled the car for 45 minutes last night and it never ticked. I was trying to get it to tick so I could rule out the fuel injector theory I have.